5.15-stable review patch. If anyone has any objections, please let me know.
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From: Zheng Yejian zhengyejian1@huawei.com
[ Upstream commit c2489bb7e6be2e8cdced12c16c42fa128403ac03 ]
There is race issue when concurrently splice_read main trace_pipe and per_cpu trace_pipes which will result in data read out being different from what actually writen.
As suggested by Steven:
I believe we should add a ref count to trace_pipe and the per_cpu trace_pipes, where if they are opened, nothing else can read it.
Opening trace_pipe locks all per_cpu ref counts, if any of them are open, then the trace_pipe open will fail (and releases any ref counts it had taken).
Opening a per_cpu trace_pipe will up the ref count for just that CPU buffer. This will allow multiple tasks to read different per_cpu trace_pipe files, but will prevent the main trace_pipe file from being opened.
But because we only need to know whether per_cpu trace_pipe is open or not, using a cpumask instead of using ref count may be easier.
After this patch, users will find that: - Main trace_pipe can be opened by only one user, and if it is opened, all per_cpu trace_pipes cannot be opened; - Per_cpu trace_pipes can be opened by multiple users, but each per_cpu trace_pipe can only be opened by one user. And if one of them is opened, main trace_pipe cannot be opened.
Link: https://lore.kernel.org/linux-trace-kernel/20230818022645.1948314-1-zhengyej...
Suggested-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Zheng Yejian zhengyejian1@huawei.com Reviewed-by: Masami Hiramatsu (Google) mhiramat@kernel.org Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/trace/trace.c | 55 ++++++++++++++++++++++++++++++++++++++------ kernel/trace/trace.h | 2 ++ 2 files changed, 50 insertions(+), 7 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 8769cd18f622f..92b381aab8f2b 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6587,10 +6587,36 @@ tracing_max_lat_write(struct file *filp, const char __user *ubuf,
#endif
+static int open_pipe_on_cpu(struct trace_array *tr, int cpu) +{ + if (cpu == RING_BUFFER_ALL_CPUS) { + if (cpumask_empty(tr->pipe_cpumask)) { + cpumask_setall(tr->pipe_cpumask); + return 0; + } + } else if (!cpumask_test_cpu(cpu, tr->pipe_cpumask)) { + cpumask_set_cpu(cpu, tr->pipe_cpumask); + return 0; + } + return -EBUSY; +} + +static void close_pipe_on_cpu(struct trace_array *tr, int cpu) +{ + if (cpu == RING_BUFFER_ALL_CPUS) { + WARN_ON(!cpumask_full(tr->pipe_cpumask)); + cpumask_clear(tr->pipe_cpumask); + } else { + WARN_ON(!cpumask_test_cpu(cpu, tr->pipe_cpumask)); + cpumask_clear_cpu(cpu, tr->pipe_cpumask); + } +} + static int tracing_open_pipe(struct inode *inode, struct file *filp) { struct trace_array *tr = inode->i_private; struct trace_iterator *iter; + int cpu; int ret;
ret = tracing_check_open_get_tr(tr); @@ -6598,13 +6624,16 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp) return ret;
mutex_lock(&trace_types_lock); + cpu = tracing_get_cpu(inode); + ret = open_pipe_on_cpu(tr, cpu); + if (ret) + goto fail_pipe_on_cpu;
/* create a buffer to store the information to pass to userspace */ iter = kzalloc(sizeof(*iter), GFP_KERNEL); if (!iter) { ret = -ENOMEM; - __trace_array_put(tr); - goto out; + goto fail_alloc_iter; }
trace_seq_init(&iter->seq); @@ -6627,7 +6656,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
iter->tr = tr; iter->array_buffer = &tr->array_buffer; - iter->cpu_file = tracing_get_cpu(inode); + iter->cpu_file = cpu; mutex_init(&iter->mutex); filp->private_data = iter;
@@ -6637,12 +6666,15 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp) nonseekable_open(inode, filp);
tr->trace_ref++; -out: + mutex_unlock(&trace_types_lock); return ret;
fail: kfree(iter); +fail_alloc_iter: + close_pipe_on_cpu(tr, cpu); +fail_pipe_on_cpu: __trace_array_put(tr); mutex_unlock(&trace_types_lock); return ret; @@ -6659,7 +6691,7 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)
if (iter->trace->pipe_close) iter->trace->pipe_close(iter); - + close_pipe_on_cpu(tr, iter->cpu_file); mutex_unlock(&trace_types_lock);
free_cpumask_var(iter->started); @@ -9311,6 +9343,9 @@ static struct trace_array *trace_array_create(const char *name) if (!alloc_cpumask_var(&tr->tracing_cpumask, GFP_KERNEL)) goto out_free_tr;
+ if (!alloc_cpumask_var(&tr->pipe_cpumask, GFP_KERNEL)) + goto out_free_tr; + tr->trace_flags = global_trace.trace_flags & ~ZEROED_TRACE_FLAGS;
cpumask_copy(tr->tracing_cpumask, cpu_all_mask); @@ -9352,6 +9387,7 @@ static struct trace_array *trace_array_create(const char *name) out_free_tr: ftrace_free_ftrace_ops(tr); free_trace_buffers(tr); + free_cpumask_var(tr->pipe_cpumask); free_cpumask_var(tr->tracing_cpumask); kfree(tr->name); kfree(tr); @@ -9454,6 +9490,7 @@ static int __remove_instance(struct trace_array *tr) } kfree(tr->topts);
+ free_cpumask_var(tr->pipe_cpumask); free_cpumask_var(tr->tracing_cpumask); kfree(tr->name); kfree(tr); @@ -10164,12 +10201,14 @@ __init static int tracer_alloc_buffers(void) if (trace_create_savedcmd() < 0) goto out_free_temp_buffer;
+ if (!alloc_cpumask_var(&global_trace.pipe_cpumask, GFP_KERNEL)) + goto out_free_savedcmd; + /* TODO: make the number of buffers hot pluggable with CPUS */ if (allocate_trace_buffers(&global_trace, ring_buf_size) < 0) { MEM_FAIL(1, "tracer: failed to allocate ring buffer!\n"); - goto out_free_savedcmd; + goto out_free_pipe_cpumask; } - if (global_trace.buffer_disabled) tracing_off();
@@ -10222,6 +10261,8 @@ __init static int tracer_alloc_buffers(void)
return 0;
+out_free_pipe_cpumask: + free_cpumask_var(global_trace.pipe_cpumask); out_free_savedcmd: free_saved_cmdlines_buffer(savedcmd); out_free_temp_buffer: diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 43058077a4def..90ab921884b10 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -367,6 +367,8 @@ struct trace_array { struct list_head events; struct trace_event_file *trace_marker_file; cpumask_var_t tracing_cpumask; /* only trace on set CPUs */ + /* one per_cpu trace_pipe can be opened by only one user */ + cpumask_var_t pipe_cpumask; int ref; int trace_ref; #ifdef CONFIG_FUNCTION_TRACER